Process for manufacturing trialkyl phosphites

ABSTRACT

A process for manufacturing trialkyl phosphite comprises adding with stirring a phosphorus trihalide at a temperature of -5* to 30* C to at least stoichiometric amount of an aliphatic alcohol having one to 18 carbon atoms in the presence of at least one of an organic acid and ammonium salt thereof while introducing ammonia to the reaction system to maintain the pH value in the system in the range of 6.5 to 10.0 to thereby effect the reaction of the phosphorus trihalide and the aliphatic alcohol to produce trialkyl phosphite. Said organic acid has a dissociation constant in water at 25* C of 1 X 10 7 to 9 X 10 5.

Bite States aten Tada et al. July 4, 1972 [54] PROCESS FOR MANUFACTURINGPrimary Examiner-Lewis Gotts TRIALKYL PHQSPHITES AssistantExaminer-Anton H. Sutto Attorney-Larson and Taylor [72] Inventors: FusaoTada, Nara-shi; Seiei lnamine,

Osaka-shi; Tsutomu Hatanaka, Sakai-shi, 57 ABSTRACT all of Japan Aprocess for manufacturing trialkyl phosphite comprises ad- Asslgnee? f fChemical Industry p y ding with stirring a phosphorus trihalide at atemperature of osaka'fu' Japan -5 to 30 C to at least stoichiometricamount of an aliphatic 22 i No 25 19 9 alcohol having one to 18 carbonatoms in the presence of at least one of an organic acid and ammoniumsalt thereof while PP N05 879,933 introducing ammonia to the reactionsystem to maintain the pH value in the system in the range of 6.5 to10.0 to thereby 52 us. Cl ..260/976, 252/493, 252/358, effect thereaction of the Phosphorus "ihalide and the 2 0 45 p 2 0 959 2 0 9 7 2 09 4 aliphatic alcohol to produce trialkyl phosphite. Said organic 5 [1lm. c1 ..c07r 9/08, ClOm l/46 acid has a dissociation constant in Waterat of 1 X to 581 Field of Search ..260/976 9 [56] References Cited 8Claims No Drawmgs UNITED STATES PATENTS 3,335,204 8/1967 Scherer et al..260/976 PROCESS FOR MANUFACTURING TRIALKYL PHOSPHITES This inventionrelates to an improved process for manufacturing trialkyl phosphiteswhich are useful as stabilizers for synthetic resins, additives tolubricants. antifoaming agents, intermediates for producing variouschemicals, etc.

It is well known in the art that trialkyl phosphites can be produced bythe reaction of phosphorus trihalides with aliphatic alcohols which isrepresented by the following equation l wherein X is a halogen atom andR is an alkyl group.

In the above reaction the hydrogen halide formed reacts with theproduct, trialkyl phosphite, to produce alkyl halide and dialkylhydrogen phosphite, whereby the yield of the desired trialkyl phosphiteis reduced. This side reaction is shown in the following equation (2):

wherein R and X are the same as defined before.

To prevent the above side reaction it is also known to use acid-bindingagents, such as alkali metal alcoholates, primary or tertiary amines andammonia. However, alkali metal alcoholates and amines are expensive, andthe use of the former makes handling procedure difficult due to thestrong basic and hygroscopic properties thereof and the use of thelatter requires very complicated procedure owing to the toxicity and thenecessity of recovery thereof. Ammonia is most econorni cal, but when itis used the undesired side reactions occur unless the ammonia exists inthe reaction system in the strictly accurate amount equimolar to thehydrogen halide formed. Namely, if the amount of ammonia in the systemis insufficient the side reaction shown in equation (2) described beforemay occur and if excess the side reactions shown in the followingequations (3) to (5) may occur.

wherein R and X are the same as defined before.

As it is extremely difiicult to accurately adjust the amount of ammoniain the reaction system without complicated procedures which requiregreat skill, these side reactions are unavoidable, reduc-ing the yieldof the desired trialkyl phosphites. To prevent the above side reactionsit is proposed to carry out at a temperature of -30 to 20C the reactionof phosphorus trihalide and aliphatic alcohol in the presence of ammonia(Cf. British Pat. No. 749,550). However, this process is not practicalin commercial production as the reaction has to be conducted at such alow temperature in spite of exothermic reaction.

As mentioned above all the conventional methods heretofore proposed arenot satisfactory for the purpose of industrial production.

One object of the invention is accordingly to provide an improvedprocess for manufacturing trialkyl phosphites from phosphorus trihalidesand alcohols which is free of the aforementioned drawbacks of theconventional methods.

Another object of the invention is to provide a process formanufacturing trialkyl phosphites of high purity in a high order ofyield without being accompanied by the undesired side reactions.

A further object of the invention is to provide a process formanufacturing trialkyl phosphites economically and on commercial scalewith simple procedures.

The above and other objects of theinvention will be apparent from thefollowing description.

The process of the invention comprises adding with stirring a phosphorustrihalide at a temperature of -5 to 30C to at least stoichiometricamount of an aliphatic alcohol having one to [8 carbon atoms in thepresence of at least one of an organic acid and ammonium salt thereofwhile introducing ammonia to the reaction system to maintain the pHvalue in the system in the range of 6.5 to 10.0 to thereby effect thereaction of the phosphorus trihalide and the aliphatic alcohol toproduce trialkyl phosphite, said organic acid having a dissociationconstant in water at 25C of l X 10'' to 9 X 10", and separating thetrialkyl phosphite thus produced from the resultant reaction mixture.

According to the research of the present inventors it has been foundthat when the reaction of phosphorus trihalides and aliphatic alcoholsto produce trialkyl phosphites in which ammonia is used as anacid-binding agent is carried out in the presence of organic acid havinga dissociation constant in water at 25C ranging from 1 X 10" to 9 X 10'and/or ammonium salt thereof the pH value in the reaction system can bereadily controlled to a constant value within the range of 6.5 to 10.0and the undesired side reactions can be efiectively prevented at areaction temperature of 5 to 30C which is far more available as comparedwith the temperature applied in the known method in which ammonia isused as an acidbinding agent, whereby the desired trialkyl phosphiteshaving high purity can be obtained in a high order of yield on acommercial scale.

The phosphorus trihalides to be used in the invention include, forexample, phosphorus trichloride and phosphorus tribromide, particularlypreferable being phosphorus trichloride.

The aliphatic alcohols to be used in the invention are those having 1 to18 carbon atoms, such as methanol, ethanol, 2- chloroethanol,isopropanol, n-propanol, n-butanol, 2-ethylhexanol, n-octanol,isodecanol dodecanol, octadecanol, etc. Among them the alcohols of l to8 carbon atoms are desirable. In the invention it is preferable to usethe alcohols in an hydrous state. In general, the alcohol may be used inat least stoichiometric amount relative to the phosphorus trihalide,i.e., in at least 3 mole per mole of the phosphorus trihalide.Preferably the alcohol is used in an excess amount of 5 to mole percentto the stoichiometric amount.

ln the invention it is essential to use an organic acid having aspecific dissociation constant and/or ammonium salt thereof. Accordingto the research of the present inventors it has been found that thedissociation constant of the organic acid is critical in the presentinvention and that only the use of the organic acid having adissociation constant in water at 25C of l X 10' to 9 X 10" and/orammonium salt thereof can effectively prevent the undesired sidereactions which are incidental to the case of using ammonia. If the acidhaving a dissociation constant of higher than 9 X 10" is used thedesired trialkyl phosphite produced may rather be decomposed by the acidused, while if the acid having a dissociation constant of lower than 1 X107 is used the undesired side reactions can not be preventedeffectively. Preferably dis-sociation constant of the acid is in therange of 5.0 X l0' to 5.0 X 10" The representative examples of theorganic acids having a dissociation constant of l X 10" to 9 X 10" are,for example, acetic acid, propionic acid, butyric acid, caproic acid,valeric acid, succinic acid, tartaric acid, benzonic acid, cinnamicacid, phthalic acid, ascorbic acid, monomethyl phosphate, monobutylphosphate, etc. Of these acids aliphatic or aromatic monoordi-carboxylic acids are preferable, the most desirable being aceticacid, propionic acid, butyric acid, valeric acid, succinic acid,phthalic acid, etc. When the acids are dicarboxylic acids, those acidsat least one of whose carboxyl groups has a dissociation constant inwater in the ra nge of 1 X 10" to 9X 10" may be used. The amount of theorganic acids to be used is in the range of l to 30 mole percent, basedon the mole of the phosphorus trihalide. Using the acid in less amountresults in poor effect in prohibiting the side reactions and in largeramount undesirable side reactions may occur due to the excess of theacid. Preferable amount of the acid to the phosphorus trihalide is inthe range of 3 to 10 mole percent.

The present process is preferably conducted in the presence of diluents,though the reaction may proceed in the absence thereof. it is alsopossible to use larger amounts of the starting alcohol simultaneouslyserving as a diluent. As the diluent can be used hexane, heptane,benzene, toluene, petroleum ether, methylene chloride or likehydrocarbons and the halogenated derivatives thereof, and ethylether orlike ethers. The preferable amount of the diluents may vary over a widerange depending upon the reaction temperature, kinds of the trialkyl'phosphite produced, etc., but it is usually used in an amount of notlarger than 400 volume based on the volume of the alcohol used and in anamount of not larger than 300 volume based on the volume of thephosphorus trihalide used.

According to one of the preferred methods of the invention, the organicacid of a dissociation constant of l X 10" to 9 X 10 may be dissolved inthe starting alcohol or a mixture of the alcohol and diluent. When theammonium salt of the acid is used in the place of or in combination withthe acid, it is preferable to introduced ammonia into the solution ofthe acid dissolved in the alcohol or in the mixture of alcohol anddiluent to convert a part or whole of the acid to ammonium salt, thoughthe ammonium salt may be directly dissolved in the alcohol or themixture of alcohol and diluent. in one of the preferred embodiment ofthe invention the starting phosphorus trihalide is then added dropwisewith stirring to the alcohol or the mixture of alcohol and diluenthaving dissolved therein the acid and/or ammonium salt thereof, whileammonia gas is introduced into the system. The phosphorus trihalide maybe added to the system as it is or in the fonn of solution dissolved indiluents. it is most preferable in the invention that the acid andammonium salt thereof coexist in the reaction system. According to thepresent invention there is no need to lower the reaction temperature tosuch low range of 30 to -20C as in the conventional manner, but areaction tem-perature of 5 to 30C which is more available is applicable.The preferred reaction temperature is in the range of to 25C though itmay vary in accordance with the kinds of alcohol used, amount ofdiluents used and other factors. The ammonia may be introduced into thereaction system so as that the pH value in the system is maintained inthe range of 6.5 to 10.0, preferably 7.0 to 9.0, whereby the reactionbetween phosphorus trihalide and alcohol to produce trialkyl phosphitecan effectively proceed, the pH value being measured by an electrometricpH measuring device. According to the invention the pH value in thereaction system can be readily controlled to a constant value within therange of 6.5 to 10.0, making it possible to produce the desired trialkylphosphite with a high purity at a high yield rate without beingaccompanied by the undesired side reactions. In practical operation itis preferable to determine the supply rate of ammonia to be introducedto the system in accordance with the supply rate of the startingphosphorus trihalide. That is to say, the ammonia may preferably beintroduced to the system at a constant rate equivalent to the amount ofthe hydrogen halide formed which is previously calculated from thesupply rate of the phosphorus trihalide added dropwise. When the ammoniais introduced at a constant rate previously determined as above the pHvalue in the reaction system is easily maintained in the constant valuewithin the appropriate value $0.5.

The present reaction completes immediately after the completion of thedrop by drop addition of the phosphorus trihalide. Usually thephosphorus trihalide is added dropwise in 1.5 to 12 hours. The trialkylphosphite thus produced can be easily separated from the reactionmixture by the conventional methods. For example, the reaction mixtureis filtrated or washed with an alkali solution to remove ammonium halidefon'ned and the desired trialkyl phosphite can be obtained by fractionaldistillation of the resultant filtrate or oil layer.

According to the present invention the reaction proceeds effectively ata temperature of to 30C which is easy to control, so that it becomespossible to conduct the reaction not only in batch system but also incontinuous manner.

For fuller understanding of the invention examples are given below.

EXAMPLE 1 In a 500 ml 4-necked flask equipped with a thermometer,agitator, dropping funnel, ammonia injection pipe and electrometric pl-lmeasuring device were placed 60.5 g (1.89 mole) of anhydrous methanol,320 ml of methylene chloride and 2.2 g( 0.03 mole) of propionic acid. Tothe resultant mixture was added dropwise with violent stirring at 0C in2 hours a mixture of 82.5 g (0.6 mole) of phosphorus trichloride and mlof methylene chloride. At the same time ammonia gas was introduced at arate of 330 to 360 ml/min, whereby the pH value in the system wasmaintained at 7.5 '1: 0.5.

After completion of the addition of phosphorus trichloride the resultantreaction mixture was washed with 0.05 N aqueous solution of sodiumhydroxide to remove the ammonium chloride formed, after which theresultant oil layer was distilled first under atmospheric pressure andthen under reduced pressure, whereby 63.5 g of trimethyl phosphitehaving a boiling point of 54 56C/100 mm Hg was obtained. The yield ratewas 85.4 mole percent. The resultant trimethyl phosphite had arefractive index of m, of 1.4095 and specific gravity of (1 of 1.053.

For comparison the same operation was carried out without the additionof propionic acid. in either operation an attempt was made to controlthe pH value in the system by severely adjusting the amount of ammoniato be introduced, but the pH value showed marked variations over a widerange of 2 to 10, and it was impossible to maintain the optimum value.By this reaction 25.8 grams of trimethyl phosphite was obtained. Yieldwas 34.7 mole percent.

EXAMPLE 2 In the same flask as in Example 1 were placed 48.0 g (1.5mole) of anhydrous methanol, 200 ml of ethyl ether and 1.5 g (0.02 mole)of propionic acid. To the resultant mixture was added dropwise withviolent stirring at 5C in 2 hours a mixture of 55.0 g (0.4 mole) ofphosphorus trichloride and 40 ml of ethyl ether. At the same timeammonia gas was introduced at a rate of 230 250 ml/min, whereby the pHvalue in the system was maintained at 7.5 10.5. After completion of thereaction the resultant reaction mixture was filtered to remove ammoniumchloride formed and the cake was washed with 200 ml of ethylether. Thewashed liquid was added to the filtrate and the mixture was distilledfirst under atmospheric pressure and then under reduced pressure,whereby 40.3 g of trimethyl phosphite boiling at 54 56C/ 100 mm Hg. wasobtained. The yield rate was 81.2 mole The resultant trimethyl phosphitehad refractive index of m, of 1.4095 and specific gravity of d2 of1.054.

EXANIPLE 3 In the same flask as in Example 1 were placed 60.7 g (1.32mole) of anhydrous ethanol, ml of n-hexane and 1.2 g (0.02 mole) ofglacial acetic acid. To the resultant mixture was added dropwise withviolent stirring at 5C in 3 hours a mixture of 55.0 g (0.4 mole) ofphosphorus trichloride and 40 ml of n-hexane. At the same time ammoniagas was introduced to the system at a rate of to ml/min., whereby the pHvalue in the reaction system was maintained at 7.8 1: 0.5.

After the reaction 55.8 g of triethyl phosphite boiling at 62 64C/23 mmHg was obtained by the same method as in Example 1. The yield rate was84.1 mole percent. The resultant triethyl phosphite had refractive indexof n of 1.4315 and specific gravity of d, of 0.969.

For comparison, the similar operation was performed except that noglacial acetic acid was used. In this operation, however it was verydifficult to control the pH value by adjusting the feed of ammonium withthe pH value varied over a wide range of 2 to 9. The triethyl phosphiteproduced was 32.1 g (yield rate of48.3

EXAMPLE 4 introduced at the rate of 130 160 ml/min, whereby the pH valuein the system was maintained at 8.0 $0.5.

After the reaction, 67.3 g of tributyl phosphite boiling at 1 19 120C/10 mm Hg was obtained by the same method as in Example 1. The yield ratewas 89.6 mole percent. The resultant tributyl phosphite had refractiveindex of n of l .43 17 and specific gravity of (1 of 0.924

EXAMPLE 5 In the same flask as in Example 1 were placed 100.0 g (1.35mole) of n-butanol, 150 ml of petroleum ether and 0.8 g (0.009 mole) ofbutyric acid. To the resultant mixture 41.3 g (0.3 mole) of phosphorustrichloride was added dropwise with violent stirring at 20C in 2 hours.At the same time ammonia gas was introduced at the rate of 170 190ml/min, whereby the pH value of the reaction system was maintained at8.2 :t 0.5. After the reaction the reaction mixture was washed withwater to remove the ammonium chloride formed and then by fractionaldistillation 66.6 g of tributyl phosphite boiling at 1 19- 120C/10 mm Hgwas obtained. The yield rate was 88.7 mole percent. The resultanttirbutyl phosphite had refractive index of u of 1.4316 and specificgravity of d, of 0.925.

EXAMPLE 6 In the same flask as in Example 1 were placed 73.3 g (0.99mole) of butanol, 1 10 ml of n-hexane and 2.5 g (0.02 mole) of succinicacid. To the resultant mixture was added dropwise with violent stirringat 10C in 4 hours a mixture of4l.3 g (0.3 mole) of phosphorustrichloride and 40 ml of n-hexane. At the same time ammonia gas wasintroduced at the rate of 80 100 ml/min, whereby the pH value in thesystem was maintained at 8.3 i 0.5.

After the reaction 67.9 g of tributyl phosphite boiling at 122 123C/ 12mm Hg was obtained by the same manner as in Example 1. The yield ratewas 90.5 mole percent. The resultant tributyl phosphite had refractiveindex of n,, of 1.4317 and specific gravity of (1 of 0.925.

EXAMPLE 7 In the same flask as in Example 1 were placed 73.3 g (0.99mole) of n-butanol, 100 ml of n-hexane and 2.6 g (0.03 mole) of butyricacid. To the resultant mixture was added dropwise with violent stirringat 25C in 2 hours a mixture of 41.3 g (0.3 mole) of phosphorustrichloride and 30 ml of n-hexane. At the same time ammonia gas wasintroduced at the rate of 170 200 ml/min, whereby the pH value in thereaction system was maintained at 8.3 10.5.

After the reaction, 66.2 g of tributyl phosphite boiling at 120 121C/11mm Hg. was obtained by the same method as in Example 1. The yield ratewas 88.1 mole percent. The resultant produce had refractive index of nof 1.4316 and specific gravity of d, of 0.925.

EXAMPLE 8 In the same flask as in Example 1 were placed 234.0 g (1.8mole) of ethyl 2-hexanol, and 1.2 g (0.015 mole) of ammonium acetate. Tothe resultant mixture 41.3 g (0.3 mole) of phosphorus trichloride wasadded dropwise with violent stirring at 20C in 2 hours. At the same timeammonia gas was introduced at the rate of 170 190 ml/min., whereby thepH value in the s tem was maintained at 8.5 i 0.5. After the reaction,114. g of tris-(2-ethylhexy1) phosphite boiling at 160 162C/0.5 mm Hgwas obtained by the same method as in Example 1. The yield rate was 91.5mole percent. The resultant tris-(Z-ethylhexyl) phosphite had refractoryindex of n of 1.4495 and specific gravity of d, of 0.902.

EXAMPLE 9 In the same flask as in Example 1 were placed 156.0 g (1.2mole) of 2-ethylhexanol, ml of benzene and 5 g (0.03 mole) of phthalicacid. To the resultant mixture was added dropwise with violent stirringat 30C in 2.5 hours a mixture of 41.3 g (0.3 mole) of phosphorustrichloride and 30 ml of benzene. At the same time ammonia gas wasintroduced at the rate of 130 ml/min, whereby the pH value in the systemwas maintained at 8.8 $0.5.

After the reaction, 112.8 g of tris-(2-ethylhexyl) phosphite boiling at160 162C/0.5 mm Hg was obtained by the same method as in Example 1. Theyield rate was 89.8 mole percent. The resultant tris-(2-ethylhexyl)phosphite had refractive index of n of 1.4494 and specific gravity of d,of 0.902.

What we claimed is:

1. A process for manfactun'ng trialkyl phosphite which comprises addingwith stirring at a temperature of -5 to 30C a phosphorus trihalideselected from the group consisting of phosphorus trichloride andphosphorus tribromide to at least stoichiometric amount of an aliphaticalcohol having one to 18 carbon atoms in the presence of l to 30 molepercent, based on the mole of phorphorus trihalide of an organic acid orammonium salt thereof while introducing ammonia to the reaction systemto maintain the pH value in the system in the range of 6.5 to 10.0 tothereby efiect the reaction of the phosphorus trihalide and thealiphatic alcohol to produce trialkyl phosphite, and separating thetrialkyl phosphite from the resultant reaction mixture, said organicacid having adissociation constant in water at 25C of 1 X 10' to 9 X 10"and being one species selected from the group consisting of acetic acid,propionic acid, butyric acid, caproic acid, valeric acid, succinic acid,tartaric acid, benzoic acid, cinnarnic acid,phthalic acid, ascorbicacid, monornethyl phosphate and monobutryl phosphate.

2. The process for manufacturing trialkyl phosphite according to claim1, in which said organic acid has a dissociation constant in water at25C of 5 X 10' to 5 X 10*".

3. The process for manufacturing trialkyl phosphite according to claim 1in which said organic acid is at least one species selected from thegroup consisting of acetic acid, propionic acid, butyric acid, valericacid, succinic acid and phthalic acid.

4. The process for manufacturing trialkyl phosphite according to claim 1in which said amount of the organic acid and/or ammonium salt thereof isin the range of 3 to 10 mole percent, based on the mole of thephosphorus trihalide.

5. The process for manufacturing trialkyl phosphite according to claim 1in which said reaction temperature is in the range of 0 to 25C.

6. The process for manufacturing trialkyl phosphite according to claim 1in which said pH value in the reaction system is in the range of7.0 to9.0.

7. The process for manufacturing trialkyl phosphite according to claim 1in which said phosphorus trihalide is phosphorus trichloride.

8. The process for manufacturing trialkyl phosphite according to claim 1in which said aliphatic alcohol has one to eight carbon atoms.

2. The process for manufacturing trialkyl phosphite according to claim1, in which said organic acid has a dissociation constant in water at25*C of 5 X 10 7 to 5 X 10
 5. 3. The process for manufacturing trialkylphosphite according to claim 1 in which said organic acid is at leastone species selected from the group consisting of acetic acid, propionicacid, butyric acid, valeric acid, succinic acid and phthalic acid. 4.The process for manufacturing trialkyl phosphite according to claim 1 inwhich said amount of the organic acid and/or ammonium salt thereof is inthe range of 3 to 10 mole percent, based on the mole of the phosphorustrihalide.
 5. The process for manufacturing trialkyl phosphite accordingto claim 1 in which said reaction temperature is in the range of 0* to25*C.
 6. The process for manufacturing trialkyl phosphite according toclaim 1 in which said pH value in the reaction system is in the range of7.0 to 9.0.
 7. The process for manufacturing trialkyl phosphiteaccording to claim 1 in which said phosphorus trihalide is phosphorustrichloride.
 8. The process for manufacturing trialkyl phosphiteaccording to claim 1 in which said aliphatic alcohol has one to eightcarbon atoms.